This invention relates generally to a vehicle control and, in particular, a light-responsive vehicle control which produces an output to operate a device as a function of light sensed by a light sensor. More particularly, the present invention relates to a control that can be used to establish the partial reflectance level of an electro-optic rearview mirror, although the invention is also applicable to a headlight activation control for activating a vehicle's headlights at low light conditions and deactivating the vehicle's headlights at high light conditions.
Light-responsive vehicle controls may include one or more light sensors which sense light conditions from within the vehicle passenger compartment. At least one of the light sensors may be directed in a particular direction, such as rearward of the vehicle. The control receives an input from the light sensor, or sensors, and produces an output to operate a device as a function of the light sensed and an operating parameter, such as a sensitivity value. The sensitivity value may be manually set, as by a user operator control, or may be set internally in the control either at a fixed level or at a variable level established by the control. In addition to light sensors directed rearward of the vehicle, light sensors may be directed upwardly or in other directions within the passenger compartment.
In a conventional electro-optic mirror control system, such as an electrochromic mirror system, a control may be responsive to more than one light sensor. For example, a control may respond to two light sensors, such as a generally forward-facing light sensor and a generally rearward-facing light sensor. The rearward-facing light sensor is more sensitive to glare, reflected by the rearview mirror into the driver's eyes, produced from light sources rearward of the vehicle. One such control is disclosed in commonly assigned U.S. Pat. No. 5,715,093 entitled AUTOMATIC REARVIEW MIRROR SYSTEM WITH AUTOMATIC HEADLIGHT ACTIVATION issued to Kenneth L. Schierbeek and Niall R. Lynam, the disclosure of which is hereby incorporated herein by reference. Such control includes a pair of light sensors, one directed generally forward of the vehicle and one directed generally rearwardly of the vehicle. The control responds to the light levels to which the light sensors are exposed in order to produce a drive signal to establish a partial reflectance level for an electro-optic mirror element and in order to produce a headlight activation signal in order to switch the vehicle headlights between an activated and a deactivated condition. In this manner, both the condition of the vehicle headlights, as well as the partial reflectance level of the electro-optic mirror, are established as a function of the light levels to which the light sensors are exposed.
It is common for vehicles to be supplied in various configurations. The vehicle is configured in this manner by some form of specification document following the vehicle through the assembly process in order to provide information for the various alternative components to be placed on the vehicle. Each alternative component is identified by a unique stock-keeping unit or SKU. Even minor differences in the characteristics of a particular component require a separate SKU so that the SKU defines a unique component. The more unique components which the manufacturer must contend with increases the manufacturing cost for the vehicle because it increases inventory expenses as well as overall record keeping expenses. Therefore, it would be desirable to reduce the number of unique components, each identified by an SKU, which must be made available for assembling a vehicle. This should not, however, limit the options available to the consumer because the availability of options is a desirable sales feature.
One optional feature which may be provided on a vehicle is tinted glazing. Tinted glazing is often optionally supplied for the rear window, facing rearwardly of the vehicle. It may also be supplied for the side windows in the rear portion of the passenger compartment. Because of safety concerns, the forward-facing window, or windshield, as well as the side windows used by the driver are not supplied with tinted glazing. Tinted glazing decreases light transitivity through the window. Therefore, glare-producing light which penetrates the rear window is attenuated by the tint which reduces the amount of light received by the rearward-facing light sensor of the electro-optic rearview mirror system. Because the partial reflectance level control responds to a ratio between the light received by the forward-facing light sensor and the rearward-facing light sensor, the presence of a tinted rear window affects the partial reflectance level established by the control. It turns out that, in the case of the interior rearview mirror, the system is self-compensating. This is because the glare viewed by the driver is also attenuated by the tint of the rear window so that the alteration of the partial reflectivity level established by the control is cancelled out by the tinted window such that the glare in the driver's eyes is the same as it would be without the tinted window.
However, certain applications do not cancel out the effect of the tinted rear window and, therefore, require different configurations for vehicles with and for vehicles without tinted rear windows. For example, the exterior rearview mirrors are viewed through the non-tinted side windows on either side of the driver. With the light sensors positioned within the passenger compartment, the response of the exterior mirror will differ dependent upon whether or not the vehicle has a tinted rear window. However, there is not a corresponding offset in glare level which would cancel out the effect on the reflectivity level caused by the tinted rear window. The result is that performance of the exterior rearview mirrors in a vehicle having a tinted rear window will be different from the performance in a vehicle having a non-tinted rear window.
The performance difference of the electro-optic rearview mirror system in a vehicle having a tinted rear window versus the performance of a vehicle having a non-tinted rear window may be accommodated by providing two or more SKUs for the electro-optic mirror system. One SKU is for use with a vehicle having a tinted rearview mirror. The other SKU is for use with a vehicle having a non-tinted rearview mirror.
Another approach has been to treat all vehicles manufactured as if they have a tinted rear window. A mirror system control is provided that chooses a different reflectivity value for the interior mirror and the exterior mirrors during transitions in reflectivity values. Transitions in reflectivity values occur such as when a glare source first becomes present, becomes stronger, or disappears. Such an approach has several difficulties. The first difficulty is that not all vehicles are ordered with tinted rear windows. These vehicles will receive a mirror system that is not optimal for that vehicle. The second drawback is that, even in vehicles equipped with tinted rear windows, the compensation occurs only during periods of transition between different mirror reflectance values. Most of the time, the mirror reflectivity values are stationary. During such periods of stationary reflectivity values, no compensation is provided for the effect of tinted rear windows.
Other light-responsive vehicle controls are also subject to affect from the vehicle configuration. For example, an automatic headlight activation circuit of the type disclosed in U.S. Pat. No. 5,715,093. The automatic headlight activation circuit in the '093 patent responds to light levels sensed from light sensors directed, respectively, forwardly and rearwardly with respect to the vehicle such that the rearward-directed light sensor senses light through the rear window. The headlights are actuated in response to light sensed by both of the two light sensors. With such headlight activation circuit, the light sensed by the rearward-facing light sensor will be affected by attenuation caused by tinted windows and, therefore, will be dependent upon the vehicle configuration.